The WebGL conformance test conformance/buffers/index-validation.html is now failing because the test was updated to reflect the spec, which is that negative offsets cause an INVALID_VALUE error to be generated.
The test was previously expecting that the large negative offset would be truncated to 32 bits and show up as a positive value.
I am not even sure that WebKit's IDL and binding generators can support long long values passed from JavaScript to C++ right now. That might be the bulk of this fix.